Meniere's disease is one of the pathological entities characterized by endolymphatic hydrops of the cochlear and vestibular labyrinths. Hydrops can result from an alteration of ion transport properties of the epithelial cells bordering the endolymphatic system. Little is known about the cellular basis of the pathologic processes involved because data from normal or pathological conditions are lacking for mechanisms of active secretion and absorption of ions and ionic permeabilities (both conductive and non-conductive pathways). This project will continue our study of ion transport by further developing and utilizing in vitro techniques with the non-sensory dark and clear cell region of the utricle. Specific parameters to be measured include transepithelial electrical potential difference and resistance, luminal ionic activities, and osmolality of the luminal fluid. In addition, vibrating probe techniques will be applied in order to identify the cellular sources and sinks of ionic current in the utricle; i.e., to unequivocally distinguish between the roles of the dark and clear cells. The membrane characteristics of the ion transporting cells will be deduced from the observed changes in the above parameters during experimental changes in the composition (including application of experimental and ototoxic drugs) of the bath or lumen of the isolated non-sensory region of the utricle.